Maize Genomics and Genetics 2025, Vol.16, No.1, 10-19 http://cropscipublisher.com/index.php/mgg 13 4 Case Study: Successful Identification of a Superior Maize Line 4.1 Background of selected maize line The superior maize line identified in this study originates from a breeding program focused on enhancing nutritional quality and stress resistance. This line, referred to as L9/T7, was developed through the inter-mating of newly introduced zinc (Zn)-enhanced inbred lines with testers from various nutritional backgrounds, including normal, provitamin A, and quality protein maize (QPM) (Matongera et al., 2023a). The breeding history of this line involves a meticulous selection process aimed at stacking multiple nutritional traits, such as zinc, quality protein, and provitamin A, to create a hybrid with high yield potential and enhanced nutritional value. The breeding program utilized a combination of general combining ability (GCA) and specific combining ability (SCA) analyses to identify superior hybrids. The line L9/T7 demonstrated positive GCA effects for grain yield and secondary traits under both optimal and low nitrogen conditions, making it a promising candidate for further development (Table 1) (Matongera et al., 2023a). This line's breeding history is marked by its adaptability to various stress conditions, including heat and drought, which are critical for maintaining yield stability in changing climatic conditions. Table 1 Estimates of lines and tester GCA effects for grain yield and other agronomic traits under managed low N and combined heat and drought conditions (Adopted from Matongera et al., 2023a) - Managed low nitrogen Combined heat and drought stress A.Lines GY AD ASI PH EPP GY AD ASI PH EPP L1 -0.07 0.37 0.40 1.47 -0.02 0.01 -0.55 -0.35 7.27 0.03 L2 -0.23 -0.03 -0.02 0.55 -0.03 -0.17 0.00 0.07 6.08 0.06 L3 -0.11 0.47 0.06 -2.26 0.01 -0.06 -0.07 -0.10 1.86 0.06 L4 -0.35 0.69 0.07 -5.96 -0.08 0.07 0.03 0.40 -11.82 -0.11 L5 -0.33 0.47 0.58 -10.11 -0.05 0.34 1.08 0.22 -8.58 -0.11 L6 0.54 -0.88 -1.06 13.39 0.10 -0.73 0.47 -0.25 4.91 0.07 L7 0.24 0.33 0.14 7.53 0.00 -0.38 0.42 0.15 1.73 0.02 L8 0.46 -0.95 -0.73 5.18 0.06 0.36 -0.28 0.43 -3.20 -0.02 L9 0.10 -0.35 0.09 -2.47 0.01 0.17 -0.16 0.00 6.19 0.06 L10 -0.10 0.33 0.32 -5.26 0.01 -0.22 -1.71* 0.32 -5.07 -0.09 L11 -0.13 -0.45 0.17 -2.06 -0.01 0.62 0.78 -0.89 0.87 0.03 GCASE 0.27 0.51 0.46 6.37 0.05 0.36 0.70 0.37 5.9 0.07 B.Testers T1 0.65 -1.77 -1.28 7.48 0.09 0.26 -0.13 -0.08 1.40 0.01 T2 0.01 -0.99 -0.37 2.30 0.00 0.29 0.00 -0.33 2.85 0.05 T3 0.06 0.60 0.44 -0.75 0.04 -0.34 -0.20 -0.02 -0.96 -0.06 T4 -0.41 1.37 0.80 -2.98 -0.09 0.14 0.24 0.03 -3.11 0.06 T5 -0.43 0.78 0.60 -11.36 -0.04 -0.61 -0.34 0.32 -8.43 -0.02 T6 0.05 0.28 0.21 1.45 -0.01 -0.30 -0.24 0.28 -0.94 -0.09 T7 0.08 -0.27 -0.40 3.85 0.00 0.56 0.66* -0.20 9.35 0.06 GCASE 0.32 1.00 0.65 5.56 0.05 0.33 0.32 0.22 4.8 0.05 Table caption: *: P≤0.05; GY: Grain yield; AD: Anthesis date; ASI: Anthesis silking interval; PH: Plant height; EPP: Number of ears per plant (Adopted from Matongera et al., 2023a) 4.2 Field trial performance The field trial performance of the selected maize line L9/T7 was evaluated under multiple stress and non-stress environments. In trials conducted under combined heat and drought stress (HMDS) and managed low nitrogen (LN) conditions, L9/T7 exhibited superior grain yield and desirable secondary traits, outperforming other hybrids (Matongera et al., 2023a). This line maintained high leaf relative water content under drought stress, which is indicative of its robust stress tolerance mechanisms (Chen et al., 2012).
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